Eternity. It works, and I like the UI.

Currently hosting XMPP:

• Group chat appears to be much better now
• Server-side caching exists now, at least in ejabberd
• Syncing also exists now, see above

As for encryption and feature support, YMMV, https://providers.xmpp.net/ has a list of servers that provide everything.

2.5 MEGA65s (R3A, R5 and R6), several vacuum tube oscilloscopes (including a 535A I restored), and a Vectrex.